Mr Cole Chemistry

DNA and Anti-Cancer Drugs

DNA & Cisplatin

Worksheet

1. DNA Structure & Bonding

The two strands of DNA are bonded together by intermolecular forces.
a. State the type of intermolecular force that holds the strands together.

Hydrogen Bonding

b. State the base pairs that are complementary to each other.

Adenine pairs with Thymine (A-T)

Cytosine pairs with Guanine (C-G)

c. State the number of bonds that the two base pairs can make with each other.

Answer:

  • C-G forms 3 hydrogen bonds.
  • A-T forms 2 hydrogen bonds.
d. The two strands of DNA are described as being anti-parallel. State the meaning of this term.

Anti-parallel Strands

The two strands run in opposite directions. The 5′ end (phosphate group) of one strand lines up with the 3′ end (hydroxyl group) of the other strand.

e. Draw a guanine base hydrogen bonded to its complementary base. Highlight the atom that bonds to the deoxyribose molecule.

Guanine-Cytosine Pair

Guanine and Cytosine hydrogen bonded
f. Draw an adenine base hydrogen bonded to its complementary base. Highlight the atom that bonds to the deoxyribose molecule.

Adenine-Thymine Pair

Adenine and Thymine hydrogen bonded

2. Nucleotides & Strands

The structure of DNA involves more than just the four bases.
a. Draw a single nucleotide of DNA that contains the base cytosine. Show on the diagram where the base hydrogen bonds to its complementary base.

Cytosine Nucleotide

Cytosine nucleotide structure
b. Draw a section of a single strand of DNA that contains the bases: adenine and thymine.

DNA Single Strand Section

Section of DNA strand with Adenine and Thymine

3. Cisplatin & Cancer Treatment

Cisplatin can be used to kill cancer cells in the body.
a. Draw the structure of cisplatin.

Cisplatin Structure

Square planar shape with bond angle 90°. The two chloride ligands are next to each other (cis).

Structure of Cisplatin
b. When cisplatin enters the cell, it undergoes a reaction with a water molecule where one of the ligands is displaced by a water molecule. Write an equation for this reaction.

Ligand Substitution Reaction

[Pt(NH3)2Cl2] + H2O ⇌ [Pt(NH3)2Cl(H2O)]+ + Cl–

c. Describe the mechanism of actions of cisplatin on cancer cells.

Mechanism

Cisplatin undergoes a ligand substitution reaction where the chloride ligands are replaced by nitrogen atoms on guanine bases in the DNA. This forms a coordinate bond between the Platinum and the DNA, causing the two DNA strands to cross-link (bind together). This kink in the DNA prevents replication and unwinding, leading to cell death.

d. Use a diagram to show how cisplatin binds to DNA.

DNA Binding Diagram

Diagram showing cisplatin binding to Guanine bases
e. State one potential side effect of cisplatin and describe how it can be mitigated.

Side Effects & Mitigation

  • Side Effects: Hair loss, kidney damage, nausea/vomiting, suppression of the immune system. (Caused by the drug attacking healthy, fast-dividing cells).
  • Mitigation: Administering the lowest effective dose, using targeted delivery to the tumour, or using anti-emetic drugs to reduce nausea.
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